Effects of Thiamin, Niacin, and Pyridoxine on Interval Growth of Excised Tomato Roots in Culture

1. The growth of excised tomato roots was determined at weekly intervals for 4 weeks when the roots were grown in culture media (a) without vitamin supplements or (b) with individual or combined vitamin supplements of thiamin, niacin, and pyridoxine. These determinations were subjected to statistical analyses. 2. Growth in all media was about the same during the first week. Little additional growth was obtained from roots grown in unsupplemented medium or in media containing pyridoxine or niacin alone. In media containing thiamin alone, or combinations of any two or three of the vitamins, growth of roots was significantly greater than in the other media. In medium containing all three vitamins, growth was significantly greater than in any other medium. Between the third and fourth weeks, however, growth in all cultures, including those fully supplemented, was markedly reduced. Hence, the best period for investigation of growth-substance effects under these experimental conditions was during the second and third weeks. 3. The data emphasize the importance of the interrelationships and balances which must exist among these vitamins in root metabolism.